我正在输入安装 xampp 的命令，但访问被拒绝。如何解决？
$ cd ~/Downloads
Downloads$ sudo su
Downloads# sudo chmode 777
sudo: chmode: command not found
Downloads# sudo chmode 777xampp-linux-x86-5.6.30.1-installer.run
sudo: chmode: command not found
Downloads# sudo chmode 777 xampp-linux-x86-5.6.30.1-installer.run
sudo: chmode: command not found
Downloads# ./ xampp-linux-x86-5.6.30.1-installer.run
bash: ./: is a directory
Downloads# ./xampp-linux-x86-5.6.30.1-installer.run
bash: ./xampp-linux-x86-5.6.30.1-installer.run: Permission denied